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Tuesday, December 15, 2009

Pre-Turbo Diesel Water Injection

Snake Oil And Water Don’t Mix

Terms like Nitrous, Super-Charging, Wastegate and other hormone-inspired phrases, leave the topic of Water-misting a little... dry; uninspiring to say the least. Water is not a fuel. By itself, water does not burn, dissociate, or otherwise directly increase engine power or fuel economy. But perhaps water does increase engine efficiency and fuel economy when it is used to eliminate or reduce waste heat processes that convert otherwise useful engine power into non-useful heat. Trust me, this heat, wherever it is created, has pump fuel as its origin energy source. That heat is fuel wasted that might otherwise go to propulsion.

The turbo is a major source of this heat. Whatever we can do to reduce heat manufacture during turbo compression will result in better fuel economy and lower exhaust gas temperatures (EGT). No snake oil claims here, just simple thermodynamic facts of life.

In this article, we will look at the facts behind the merits of pre-turbo diesel water injection (PTWI) as a pre-emptive cooling mechanism: a means to tame that waste heat mechanism and direct that energy to the wheels.

The Power of Disappearing Water

Your body is an engine: an organic power plant. How quickly a large room goes up in temperature when a crowd of people pile in. Water is our coolant. If we could not sweat, our temperature would never be held down to 98.6ºF. Water is essential to heat control for all life and living things. So how about applying this power to an overworked diesel engine?

One day, I was towing on an eight percent grade, headed for a downpour. I was listening to my fan roar and watching my coolant temperature rise. The rain lasted maybe 30 seconds, but 15 seconds in, I noticed a funny thing. My fan had quit running and my temperatures were near normal. Sure enough, as I exited the shower, the fan and the temperature spikes all began again. There was no question that the rain had effectively cooled my engine – if only for its brief duration.

Something similar happens to my body when I cycle in the desert. With its eight percent humidity, outdoor desert activity at 112ºF is lip blistering. Heat stress can quickly turn into fatal heat stroke as quickly as four hours after the onset of heat stress symptoms. On non-monsoon days, I pedal through this near lack of humidity and 112ºF in a white absorbent cotton long sleeve shirt. I carry two liters of water on my back and I can go through most of it within two hours. At the first sign of nausea or weakness, I get wet, no delay. Air conditioning on the fly: and it is amazingly effective.

I was deep into the Sonoran Desert on my mountain bike at 108ºF when a monsoon storm came in from the East. In the distance, a wall of dirt could be seen advancing toward South Mountain and the breeze was whipping up.

“This should be a treat,” I thought to myself.

I had seen it many times, but usually from the radar display. This time I was caught out. Soon, wind-driven dust filled my eyes. The wind eventually gave way to rain: it came down so hard it hurt. I circumnavigated the lower relatively dry washes – which were filling up fast – and narrowly escaped being stranded; getting across the main wash before it flooded. By the time I drove through the final mile of water crossings, the storm had nearly passed.
Prideful and tattered, I arrived home to see my neighbors looking skyward from safely inside their open garages.

“But it’s a dry heat!” I yelled sarcastically, with arms spread like a stage win at the Tour de France.

“Experimenting with the meds again?” they replied.

I stepped into the shelter of my house to ponder the cooling power of water that I had just witnessed firsthand. When I had started my ride, it had been 112ºF, intolerable except for the water I had ported with me: now it was 86ºF and I was shivering. A 26ºF drop in less than one hour. Why?

Driving with a Tailwind

Here is a thought. Our vehicle, in stock configuration, is, at best, 35% efficient. For every three gallons of fuel burned, only one gallon actually turns the wheels. The other two gallons, 65%, is wasted. Much of that goes out the exhaust as heat. However, some of it is heat energy wasted in non-propulsion heat processes such as the heat generated during the turbo’s compression process. Imagine if we could redirect even ten percent of those two gallons back to the wheels? That would mean that our 35% efficiency could go to 45%. In theory, that would represent a 30% increase in fuel economy (45/35=130%). In other words, anywhere we can find and eliminate a waste heat process, our effort should be rewarded nearly three-fold. Who doesn’t like driving with a tailwind?

The biggest waste heat process we find in any forced induction vehicle is in the turbo-charger compression process. More specifically, the more compression that you try to squeeze out of the turbo, the more parasitic and heat producing it becomes. When you are making 400 HP with the help of an inefficient turbo at high elevation it will manufacture 475,000 BTU per hour of heat from the compressor. That heat – the power experienced by the turbo shaft, albeit with very low torque and very high (140,000) RPM – is the wheel power equivalent of 200 HP! That power has to come from somewhere: it comes from the conversion of exhaust heat to mechanical turbine work. For a better explanation, see Thermal Feedback explanations in former issues of maxxTORQUE.

Putting Out The Fire

This is where diesel water injection gets exciting: extreme turbo shaft activity. Here is an excerpt from Aircraft Gas Turbine Powerplants Handbook:

The injection of water into the gas path causes heat transfer. When the fluid evaporates, heat in the air will be transferred into the fluid droplets, cooling the air and making the gas-flow more dense. Diesel water injection in a gas turbine engine is then a means of augmenting engine thrust. Augmentation can be thought of as occurring in two ways.

First, addition of water to air in the compressor increases compression and mass flow.

Second, water cools the combustion gases which allows additional fuel to be used without exceeding maximum temperature limits... Increases in these three engine parameters results in a thrust increase in the range of 10 to 15 per cent.

Pilots, whose lives have depended on it, have seen it first hand. World War II fighters used anti-detonation injection – the common term in the aircraft world for water injection – to improve performance, permitting escape to higher altitude. Water injection helped launch B-52G Bombers with 200,000-pound weapon loads into Vietnam.

The injection of water droplets into compressor inlet ducting is now commonly used as a means of boosting the output from industrial gas turbines. The chief mechanisms responsible for the increase in power are the reduction in compressor work per unit flow and the increase in mass flow rate, both of which are achieved by evaporative cooling upstream of and within the compressor… Consideration is also given to the efficiency of the compression process... (J. Eng. Gas Turbines Power – October 2004 – Volume 126, Issue 4, 748)

In the case of an eight-engine B-52, you get more thrust. With our trucks, more torque.

Keeping EGT Under Control

We monitor EGT as an important heat stress indicator. Exhaust gas temperature must be controlled or things melt. When the engine has to work harder (to fund waste heat processes), EGT is unnecessarily high, a longevity concern. Factory tuning usually insures it will be sufficiently low. When we get brave and decide to up the power, we introduce more fuel and, as a result, higher EGT. It can easily go from 1,200ºF to 1,400ºF – even higher in an aggressive tune. Much like desert survival, water can be used in the engine to stay within limits. By breaking the bonds that hold water molecules together, the surrounding temperatures (EGT) will lower. This breaking of water molecule bonds is evaporation.

Evaporation: Effective Heat Control

One BTU is the amount of heat required to change the temperature of one pound, or two cups, of water one degree Fahrenheit. Interestingly – and important to diesel water injection – each pound of water converted to vapor requires nearly 1,000 BTU (970 to be exact). In other words, evaporating water uses the amount of energy required to heat up that same water 970ºF. The energy consumed during evaporation is referred to as the Latent Heat of Evaporation: water has one of the highest on the planet. Since water is cheap and stable at atmospheric pressure, it is the perfect substance for internal cooling, for your body – and for your engine.

A 40 gallon bathtub requires 8,000 BTU of heating in your water heater, yet only one of those gallons (eight pounds) needs to evaporate to cool it all the way back to room temperature

Five 60 watt light bulbs consume 1,000 BTU in one hour

To burn 1,000 BTU anatomically, you have to exercise aerobically for two hours 1,000 BTU is one ounce of diesel fuel burned, producing 300 HP for five seconds. The amount of energy-absorbing potential available in two un-evaporated gallons of water is enough energy to run a marathon.

The cooling needs of an eight cylinder turbo-diesel at 70 MPH can be met in the energy absorbed from evaporating just one cup of water every minute.

Maybe the best analogy: if your clothing was soaked with water on a 60ºF, no humidity day, with a 20 MPH wind, by the time two cups of water evaporated (970 BTU) off your clothing – about 20 minutes – you would be left fighting for life with a dangerously hypothermic 92ºF core temperature.

Clearing the Fog

With water such an affordable and plentiful material, it seems foolish to neglect to take advantage of it as a means to help meet our power and efficiency requirements. Unfortunately, there is so much confusion surrounding water injection. The main reason for this confusion is lack of understanding about how it works – and how to make it safely work for you.

Most water injection kits are applied to spark ignition vehicles. The main improvement realized through water injection for these vehicles is that the water droplets that enter the combustion chamber lower the combustion temperature, inhibiting the automatic knock/detonation timing retard that occurs in closed loop ECU timing control. Since the vehicle can then maintain more advanced timing, more power is produced. These protection mechanisms do not exist on the diesel PCM software, so this type of misting has less merit. All that detonation suppression and computer timing retard yada yada is simply not relevant to a diesel. There is no IAT-knock timing retard algorithm, so if you are accustomed to gasoline knock and octane concepts, fuel-water ratio, etc, dump these concepts and forget everything you have been taught in order to apply this technology to your diesel.

Nine Myths of Pre Turbo Diesel Water Injection

To begin, we will look at some of the myths and truths that surround pre-turbo diesel water injection…

MYTH 1: Water Injection creates a condition where hydrogen and oxygen are liberated in the combustion process, thus making more power.

TRUTH: I came across this claim by a prominent diesel performance manufacturer. Presumably, we are left to believe that the dissociated hydrogen and oxygen are responsible for the power boost: this is, at best, simply untrue. The energy required to split the components of water, is unimaginable. If it was that easy to do with heat, we would all have water in our fuel tanks! Hydrogen and Oxygen gas are not created from water as part of the diesel water injection process.

MYTH 2: When water is evaporated, it creates steam which displaces air resulting in less oxygen being available for combustion.

TRUTH: When water goes to gas state, the resulting air flow rate and oxygen density increase along with the cooling effect. We will prove this later.

MYTH 3: I live in a high humidity area, I would not benefit from water injection.

TRUTH: No matter the ambient humidity, the relative humidity of the same parcel of air, after compression, is much lower. In fact, relative humidity can lower to only a tenth of ambient humidity, permitting more water to be evaporated. Also, in elevated areas, humidity is seldomly greater than 20%. Why do I bring this up? Because induction cooling is needed most at higher altitudes where compression heating is at its worst. Naturally occurring low humidity at higher elevations plays right into our hands.

MYTH 4: Pre turbo diesel water injection will destroy my compressor.

TRUTH: No question, poor application can erode the compressor, but from my experience, it is also true that 99% of pre-compressor misting is done improperly. If you follow the examples set by all the poor applications so prevalent in the industry, you can damage your compressor too. Still, too few of us understand that water cooling could actually prevent that turbo explosion that resulted from a 36 PSI overspeed.

MYTH 5: The evaporated water will re-condense in the CAC, posing a pooling and hydro lock threat to the motor.

TRUTH: This one you will see on every internet forum that discusses water injection. I could go to the psychrometric chart to demonstrate, but let’s just rely on just a little common sense. At max power and air flow, air is running through the CAC at over 100 MPH and in a temperature range of 200 to 500ºF. Is it possible for anything to pool in this environment? Of course not. However, if water flow occurred at idle, because of siphoning, or worse, engine off, due to a malfunction, there is a problem. The mixture that enters the cylinder must remain compressible, that is, in a gaseous state. If too much liquid water enters during the intake stroke, it becomes an incompressible obstacle preventing the piston from reaching a fully compressed state, with subsequent catastrophic rod-bending stress. Failsafes must be used to prevent this solitary danger.

MYTH 6: Water will corrode the aluminum CAC from the inside out.

TRUTH: If so, intercoolers in foggy low lying areas all need to be replaced. Done in moderation, liquid water need never see the inside of a CAC more than what is experienced on a cold, wet morning. Diesel water injection is typically activated less than one percent of total operation, and even then it is under high heat conditions. Any moisture wetting the CAC in this short duration spray is gone within seconds of the end of spray. It would take days or weeks of constant exposure to water for oxidation to occur significantly. Typical spray duration exposes the CAC to much less water than operation in wet humid environments, by far. Methanol mixtures are no worse.

MYTH 7: For water injection to work well, the water needs to be cold.

Truth: Widely misunderstood. The energy absorbed to evaporate a pound of 80ºF water is 700% more than required to heat (or cool) that same water by 100ºF. Cooling the water first is too much trouble for too little benefit.

MYTH 8: For water injection to work well, the water must be hot, closer to its boiling point.

Truth: Water evaporates at all temperatures. If it didn’t, puddles would never dry, little Johnny would always be soiling the carpet with muddy feet, and the kitchen floor would be perpetually wet after mopping. It does evaporate more quickly near its boiling point, but this point is a minor one.

And my favorite...

MYTH 9: Pre-compressor diesel water injection reduces the efficiency of the intercooler.

Truth: It is not a myth. This is a physical fact – and, quite seriously – so what? It is irrelevant. The idea here is that CAC efficiency, by definition, is dependent on the inlet temperature conditions being as high as possible. Subtract ambient air temperature from Compressor Outlet Temp (COT), a larger number means higher CAC efficiency. So lowering COT, the result of using pre-turbo water injection, means the CAC is less utilized. A bad thing? In the end, what is important is charge temperature and density entering the cylinder. Opponents of WI usually argue that it is better to let the CAC do its job and then apply evaporative cooling. I disagree. That approach completely disregards two very important known observations.

1. It ignores all the other benefits of pre-compressor water injection to the (parasitic, heat creating) turbo compression process itself, which handily outweigh this small point, and

2. There is no practical way to evaporate significant amounts of water after the compressor, making for a mute argument, one without any legs.

Because of these myths, pre-compressor diesel water injection has a bad reputation. I say that the bad rap has resulted from the fact that it is rarely ever implemented correctly.

Water Properties that Aid Diesel Water Injection

Understanding some of the properties of water will help us understand how it can be effectively used to cool our diesel engine.

Imagine an industrial fire. The fire crew pulls up to the scene, sweat dripping as they struggle to unfold the same flat line they have carefully stowed a hundred times. Finally, the engineer turns a wheel or two and the line quickly becomes round, revealing a high pressure projectile stream spewing 150 feet before hitting the target. And then, in an act of defiance, 90% of the precious water collects under the fire and runs right off the sight and into the sewer. This phenomenon occurs as the result of water’s surface tension property. With surface tension, if you fill a glass with water, you will be able to add water slightly above the rim of the glass without spilling over. Surface tension slows the evaporation process.

Water’s surface tension is caused by the inward pull of Hydrogen bonds at the water’s surface. This property is what causes water to form a sphere – or on a flat surface a hemisphere – or stand above the top of a glass. Surface tension slows the evaporation process. In order to get the most out of water injection’s cooling effectiveness, surface tension can be reduced by mixing it with other liquids such as methanol.​

A downpour in the Sonoran Desert significantly reduces otherwise scorching temperatures through the power of evaporative cooling. If disappearing water can reduce heat on this scale, then there is hope for the desert-like conditions in side your diesel engine.

In liquid water, the individual water molecules are all held together in a three-dimensional lattice by the Hydrogen (H) to Oxygen (O) attraction.

HHO—HOH—OHH

Each molecule is simply two Hydrogen atoms and an Oxygen atom but with different alignments. They are bonded together, Hydrogen to Oxygen by Hydrogen bonds, represented by the red arrows in the drop of water in the graphic above.

Inside a drop of water, a few molecules away from the surface, each molecule is engaged in a tug of war with its neighbors on every side. For every up pull there is a down pull and for every left pull there is a right pull and so on, so that any given molecule feels zero net force. At the surface, things are different. With only air above, there are no water molecules to pull up; as a result, the net force on the surface molecules is directed into the liquid. This force asymmetry causes the water surface to bend and ultimately form the shape of a sphere. The water’s stretchy-skin-net-like effect is called surface tension, the fire crew’s enemy. It is the property of a fluid that pulls it together, to collect and pool, instead of disperse and provide coverage. It readily forms streams, ponds and runs downhill.

The same detergents that helps water to clean clothing also helps water to put out petroleum fires. The key to extinguishing fires is coverage, creating a barrier between the fuel and the oxygen. With petroleum fires, pure water is heavier than the fuel, sinking and pooling beneath petroleum on contact. As a result, water must be treated with a foaming agent. The foaming agent (surfactant) forms bubbles in the water, giving it the lightweight floating property to stay on top and suffocate the petroleum fire.

Breaking the Ties that Bond

Relative humidity, a variable property, is the measure of how much water vapor is in the air relative to how much total water vapor the air is able to hold. It is expressed as a percentage. If we expose dry air (0% relative humidity) to liquid H2O, the air will absorb water molecules as they evaporate, each water molecule setting up residence between oxygen and nitrogen air components. Only so many H2O molecules can fit. When no more water molecules can fit among the air components, the air is saturated (100% humidity). At that point, any additional water remains liquid. Once the air mass is saturated, there is a simple way to increase its capacity to hold more vapor: heat it. If you heat it up, the air mass expands and allows more room for more water molecules. Now it will take on more water (if you are getting ahead of me, you already realize this is what happens under hood.)

Steam Me Up

I said I would explain where the energy comes from for evaporation. Each H2O molecule can have four bonds to other H2O molecules. In order for just one surface water molecule to evaporate, all four of these H-O bonds must be broken. Breaking these bonds takes energy. You can deliver this energy in the form of heat, by heating it on the stove top for instance; or, to a lesser extent, evaporation will occur spontaneously and invisibly at lower temperatures. The energy for this comes from the air and water itself, in turn lowering the temperature. This latent heat removal is commonly called evaporative cooling and is the crux of this article.

Watch a drop of water sitting on a freshly waxed hood. Its compact, hemispherical shape is a big deterrent to air stream evaporation. It is the perfect shape for minimizing surface area: the air-water interface area required for evaporation to occur. This same drop will be gone quickly if it is spread across a chamois because it will have taken on a much larger surface area. To achieve a decent cooling rate we need to do everything we can to promote evaporation. Increasing the surface area of the water will help us toward that goal. Swamp coolers do this by soaking a wicking cloth in water and passing the air through it. Another common method is fogging: the water is forced through a small orifice at extremely high pressure, creating billions of micron sized droplets which evaporate quickly because of the shear number and overall increased surface area. In order for water injection to be effective, we must do the best we can to increase the surface area of the water we are injecting and, by doing so facilitate quick evaporation.

Time is Not on Our Side

We must do this because the biggest challenge in accomplishing what we want is time or, more precisely, the lack of very much of it. Air travels from airbox to cylinder, sometimes, in under a second. A typical 60 micron droplet requires 10 to 15 seconds to evaporate when adrift, though it varies depending on air humidity, temperature and motion. If air stagnates around the drop then the air layer immediately adjacent to it will become saturated. Getting the air and water droplet to interact more leads to quicker evaporation. This causes that adjacent saturated layer to be continuously replaced with dry air. Remembering the chill at the end of my desert ride, I will say that this is why hypothermia is accelerated with wind. Our droplet needs a breeze.

Even better, how about a 600 MPH, 400ºF breeze? The 120,000 RPM compressor is a blender with incredible cyclonic effectiveness. Small droplets that hit the compressor are immediately pulverized into thousands of smaller microscopic foglets as they are swept through the storm created by the turbo. The total surface area of water exposed to air is instantly 1,000-fold that of the best post-CAC installations. These sub-micron sized droplets, mixing with air at 600 MPH, are then flash vaporized in the 400ºF degree compressed air environment.

Compressor Blade Impingement Irony

During normal use, a vehicle would rack up just 30 minutes of injection over 10,000 miles, even for those of us that tow frequently, the number would be less than two hours. SAAB implemented a factory pre-turbo misting system. They reaped 15 to 20 HP (over 10%) on water alone with a two liter displacement. You can do the math for your own application. These turbos were inspected in a test program and guess what? It caused compressor blade erosion. Yup, after 100,000 miles, and with the aid of a ten-power lense, there was enough erosion to predict a useful life of only – wait for it – 200,000 miles. They were returned to service without any performance degradation. What is most impressive is that these same turbochargers, previously capable of only 20 PSI, could output 24 to 26 PSI with water. Fair tradeoff? At these overspeed levels, the useful life of the same turbo without the benefit of this cooling was only 60,000 miles.

So, it is a bit ironic that people condemn pre-compression diesel water injection for its one inherent disadvantage, when it doubles the overall life of your turbo as a unit. If you are going to grenade your turbo in overspeed self-destruction, why would you ever worry about slow erosion to an affordable and replaceable part caused by a process that is proven to increase longevity of your turbo at these levels?

Reality Check

An interesting study found water injection to be quite safe in axial compression where peak tip velocities are similar to what we would subject a turbo compressor to:

Prior experience with wet compression systems that have operated on other large frame industrial combustion turbines has shown that most erosion occurs on the leading edge of the row one compressor blade producing a slight change in chord length (approximately one millimeter) over 24,000 hours of wet compression system operation. However, this wear was not extensive enough to require blade replacement at that interval. Stationary compressor vanes are expected to see some loss of coatings and roughening of the surfaces that are wetted, but have not shown a change in chord length. Downstream stages of rotating compressor blades will also show signs of erosion in the tip region over time, as the water droplets are centrifugally forced outward. This continues until the water is fully evaporated around the fifth or sixth compressor stage. Caldwell Energy

Lose-Lose Design

That said, the typical water injection system design neither minimizes the effect of compressor blade impingement nor functions in a way that maximizes surface area of the injected water which, as we have already seen, would yeild more effective cooling. Instead, the misting nozzle shoots across the pre-turbo intake. In fact, every designer of these systems makes the exact same mistake: a single high volume nozzle is positioned so that it is aimed at the opposite wall of the tube. The mist shoots out at 100 MPH, 100-micron diameter droplets: 20 times larger and 50 times heavier than fog. Most of the droplets immediately collide on contact with the wall’s surface and, thanks to surface tension, recombine. The resulting re-formed steady stream of liquid then gets dragged along the wall and into the fastest part of the compressor, the tips. These blade tips are bombarded and eventually erode where the stream meets the blade. If you see how this happens, it is not too difficult to design a more intelligent – and much more effective – diesel water injection system.

Heat From?

A wedge of air is ingested between each adjacent pair of compressor blades. When spinning at 100,000-plus RPM, the air is subjected to huge centrifugal forces as it moves from the center of the impeller toward the blade tips: compression. Consequently, the molecules are forced closer together as it gets near the volute exit where T2 is measured. A lot of internal friction occurs in this process. Near the tips of the compressor, air approaches sonic speed. The frictional heating that results makes the air try to expand, increasing the pressure. This resists what we are trying to accomplish, the outward movement of the air. Eventually a balance is struck between the centrifugal forces trying to throw the air out of the impeller and the back-pressure build up due to the compression and heating. The whole process takes a millisecond.

The addition of water, with its enormous latent energy absorption potential, removes a large fraction of the heat-induced pressure gain. Frictional heating and expansion is reduced and T2 is also reduced. As a result, more air can exit the impeller over a given period of time and more of the pressure gain is real compression instead of waste heat. With this cooling (contraction), the lower air velocity lessens the resistance losses in the entire tract.

Technically…

Have you ever noticed that your vehicle operates more strongly, coolly and responsively when running through a fog? When I lived in northern California, my twin turbo loved the cool mist mornings. In thermodynamic speak, what happens in fog is the result of more isothermal (constant temperature) compression which is more efficient than adiabatic compression. The work of compression is:
W(c) = m Cp (T2 – T1)

Lowering T2 (exit temp) through evaporative cooling from fog reduces the effort (work) that is required to turn the compressor. In other words, it will turn more slowly, while producing the same boost, only cooler, denser boost. Or you can apply the same turbine work and get more boost. Boost production has the highest heat consequences at higher elevations where air is almost always dry and never foggy – the humidity paradox. So you need to bring the fog to your turbo. But how much?

Psychrometric Chart

The Psychrometric Chart, although kind of busy, is useful; it describes the physical and thermal relationships of moist air. It will let us predict how much water to use, without any formulas.
Consider a heated air parcel: it expands and becomes less dense. The air molecules get further apart, allowing more room for water molecules to fit. Relative humidity decreases, even though actual water content stays the same. Then as more water is injected and introduced through evaporative cooling, the temperature comes back down, shrinking the air parcel. The evolving water molecules inhabit quickly shrinking (cooling) real estate and soon it saturates again.

We can track this process in a couple of simple problems.

Problem 1: On an 80ºF day, relative humidity is 60%. Under the hood, the air is heated 40ºF before it reaches the compressor. Plot the humidification of this air assuming enough water to reach 100% saturation.
(For anyone towing in high elevations, 60% relative humidity is very conservative, 10 to 20% is a more typical number. If you live in the Desert Southwest, as I do, 60% happens about three times a year, so it is very conservative.)

1. Plot our initial conditions: an 80ºF day with 60% humidity. Note, some of the properties of this air. The air’s density is 0.0719 pounds per cubic foot (the higher the better).

2. 80ºF is the ambient condition. But because of engine heating and radiation, actual intake air box temperature is usually higher. Let’s say it is heated up 40ºF to 120ºF. This is typical. So move to the right to 120ºF; now, the density has lowered to 0.06711 pounds per cubic foot. Humidity has dropped from 60% to 17%.

3. When we fog the air and evaporate water to saturation, enthalpy (diagonally on the chart) is held constant since we are not adding or removing (total) energy from it. The energy supplied to the water for evaporation is taken from the air surrounding the injected water. So following the dashed constant enthalpy line, it arrives at 80ºF and density increases to 0.0714 pounds per cubic foot dry air, a six to seven percent increase in dry air (and oxygen) density. This air density is almost what it was before being heated under the hood. This is a key point. This shows that with even modest amounts of air charge heating, high humidity quickly becomes low humidity, which can be cooled through water injection. Myth #2 busted.

Problem 2: Using the plotted chart, how much injected water is necessary for saturation?

Go to the right side axis. Our 60% humidity air starts out at 0.013 pounds moisture per pound of air. At full saturation, moisture content has increased to 0.022 pounds. 0.022-0.013 or 0.009 pounds of water must be injected for every pound of air in order to obtain 100% humidity. Our turbo-diesel typically uses 50 pounds per minute of air. So we need to mist 50 x 0.009 or 0.45 pounds (eight ounces) of water each minute. Keep in mind, this is a high humidity example. In the Rockies, rarely is humidity over 10%, just like my Desert. If you run this chart again for those dryer conditions, you will see that saturation is reached with 16 to 24 ounces per minute and additional temperature reduction (increased density) which is really important in this rarefied environment. If you run higher boost in your tune there is more air flow, so 30 ounces per minute might be required.

A 40% reduction in humidity occurred with a mere 40ºF under hood temperature increase. And this is on just the cold side of the turbo compressor, before compression heating. Now imagine what happens to humidity after 20 PSI of compression and the 300ºF temperature increase that comes with it. With full boost, temperatures routinely exceed 400ºF. For racers who are maxing out small stock turbochargers or for those of us towing heavy in high altitudes, temperatures easily reach 500ºF! I have logged 590ºF near sea level. That is basically 0% relative humidity.

100% outdoor humidity becomes a bone dry 3% at 400ºF. Air at this temperature will absorb a lot of evaporated water. This makes pre-compressor fogging the single best location to begin conditioning the air regardless of the ambient humidity levels in which you typically drive. It is your one shot at massive chemical intercooling using latent heat affects.

Too many pre-turbo water injection designs have given the concept a bad reputation. The intelligently designed I-Fog (above) uses multiple small nozzles and axial injection to maximize PTWI’s effectiveness on your turbodiesel.

Water-Only Limitation

We are compressing air up to 30 PSI in the turbocharger. Exiting the compressor at this pressure on a hot day, COT is 500ºF. We want that air to be as cool as possible before entering the cylinder. The typical heat soaked CAC will bring it down to 250 to 300ºF on a hot day. Water can cool it down to 300ºF if enough water can be evaporated. To bring it to 300ºF, our 200ºF desired reduction, we refer to the usual heat balance equation:

To do this by evaporating water, at 1,000 BTU per pound, we need 210 pounds of water per hour or three pounds per minute: around one to two quarts per minute. But in reality, as the air is cooled, it quickly saturates well before that much water can be evaporated. That might impose a limitation, hypothetically 100,000 BTU per hour on how much evaporative cooling is possible with water. How do we get around this limit?

It Only Works If You Work It

So far, everything we have discussed centers on water alone. As the world’s universal solvent and almost cost-free element, it deserves the lion’s share of the practical discussion. But what happens when I mix in another solvent, like alcohol? How will that affect cooling? Will it interfere with water evaporation?

Each solvent has its own physical properties. Alcohols, for example, boil at lower temperatures (aromatic) than water, so they evaporate more quickly, a good thing for cooling. Alcohol, when mixed with water, has no idea what the humidity is, and it does not care. It evaporates on its own alcohol saturation schedule with little regard for the adjacent water molecules. As far as the alcohol knows, air with 100% humidity is irrelevant. Alcohol gas will saturate the air parcel separately on an independent gas saturation mechanism. So if you mix water with methanol, 50/50, you should now be able to evaporate double the amount of mixture since only half of it is water. As a result, there is significant additional temperature drop potential as well – up to another 100ºF – some of it prior to the compressor.

In other words, if one gallon per hour of pure water was calculated, then two gallons per hour of 50% water/50% methanol will evaporate just as readily, with a large increase in the cooling effect compared to water alone. Get some rubbing alcohol and give yourself a sponge bath with it under a ceiling fan. You will get the idea.

An added plus with some solvents is that the surface tension of the water-based mixture is often reduced. Just 10% methanol, for example, drops the evaporation-inhibiting surface tension 30%. The viscosity decreases as well and this means a higher nozzle flow rate, smaller droplets, less agglomeration and increased evaporation rate. More surface area, more evaporation, multiple evaporation mechanisms, multi-solvent evaporative cooling. Nothing else does this with so little operational cost.

Fueling Speculation

Plus methanol is a fuel – adding to our power requirements. But does this mean that it is safe?

Rudolph Diesel designed our combustion cycle based on chemical-free air being compressed and heated in the cylinder: this heat auto-ignites the ensuing spray of diesel fuel near maximum compression. Auto ignition is the spontaneous, yet predictable firing of the air fuel mixture from the heat developed by the cylinder compression itself.

The inherent ignition delays built into this cycle are important and must not be overly compromised. I assert a simple philosophy here that originates from nothing more than an intuitive reality. In my mind, being unfaithful to this detail may cost you your engine.

Diesel ignition must remain under the control of your ECU.

OEM timing algorithms assume that only air is used, not ignitable gases like methanol vapor. The moment you introduce flammables and combustibles into the charge air stream of a diesel, you have potentially compromised the inherent safety net of a cycle that relies on the ingenious simplicity of pure air (oxidizer only). Simply put, if the air charge (with vapor fuel mixed in) ignites before diesel auto-ignition, ignition timing will be advanced to a point that can cause premature and massive cylinder pressure.You can inadvertently bend rods or, less seriously, convert your head gaskets into mush. But as long as the ECU-controlled, diesel auto-ignition mechanism is the ignition source for your charge fuel, there will be no problems. Don’t let the tail wag the dog.

Di-ethyl Ether (starting fluid) is an example of this with the 320ºF number in the table below. It will ignite as soon as it hits a live glo-plug. Even if they are de-energized, if you were to feed ether into the air supply of a warm diesel, it will ignite well before TDC causing the piston to try to turn the motor backwards. If a large amount is sprayed, you will have severe damage to fix. Find the starter fluid can in the garage and the warning on the can that reads something like, Never use this product on a warm motor.

Ironically, diesel fuel is another example with a low auto-ignition temperature, about 450-480ºF, and this is by design. If diesel were in the cylinder on the compression stroke, it too would ignite prematurely. I met someone who decided to prove just that by putting diesel vapor in the air tract: it lasted a few seconds. He eventually replaced his injectors with larger ones, sometime after the $3,000 overhaul.

All About (Pure) Methanol

If we are going to use it, we need to understand it. The last thing I want to do is pretend that it is harmless. Some diligent prevention here can potentially save a lot of facial hair.

General Description: A colorless, fairly volatile and flammable liquid with a faintly sweet pungent odor like that of ethyl alcohol. The vapors are slightly heavier than air and may travel some distance to a source of ignition and flash back. Any accumulation of vapors in confined spaces, such as buildings or sewers, may explode if ignited. Used to make chemicals, to remove water from automotive and aviation fuels, as a solvent for paints and plastics, and as an ingredient in a wide variety of products (NOAA Reactivity, 2007).

Flash Point – (lowest temperature at which a liquid gives off enough vapor to be ignited at its surface) 52ºF

Lower Explosive Limit – (lowest concentration of a flammable vapor in air at which explosion or combustion can occur) 6%

Upper Explosive Limit – (Highest concentration of a flammable vapor in air at which explosion or combustion can occur) 36.5%

Auto-Ignition Temperature – (the lowest temperature where the component ignites without any ignition source) 867ºF

Specific Gravity – 0.792 at 68.0ºF (USCG, 1999)

Vapor Pressure – 100.0 mm Hg at 70.2ºF; 237.87 mm Hg at 100ºF

Boiling Point – 148.3ºF at 760 mm Hg

Molecular Weight – 32.04 (NTP, 1992)

Auto-Ignition

This color table below helps characterize the risk for your diesel when a given fuel is introduced into the charge air stream. Green fuels (850-1100ºF) are relatively safe. Yellow fuels (550-849ºF) need careful scrutiny. Red fuels (0-549ºF), like ether, are a surefire way to run over your crank.

The yellow zone represents compounds that must be carefully administered. To use them in the charge air stream, the temperature of the charge stream must be closely controlled, because if these compounds become too warm before cylinder compression, they can take on the auto-ignition dangers of red compounds when compressed. A 550ºF compound must be used more carefully than a 850ºF compound.

Fuel Auto-Ignition Temperatures

Fuel

(ºF)

Diethyl ether

320

Fuel Oil No.1

410

n-Heptane

419

n-Octane

428

n-Hexane

437

Diesel No.2

480

n-Pentane

500

Gasoline

536

Ehtyl Alcohol

689

Isopropyl Alcohol

750

n-Butane

761

Propane

842

Methyl Alcohol

867

Hydrogen

932

Coal-tar oil

1076

Methane (Natural Gas)

1076

As compression occurs, the new fuel impregnated, combustible air charge, gets heated to 900-1,000ºF at TDC, the exact number depends on the compression ratio and the cylinder inlet air temperature, IAT, then subtracting our evaporative temperature drop. The question that needs answering is when will it combust, compared to diesel ignition?

Use Only Under Adult Supervion

Is methanol safe to handle? I admit that when I have to visit the emergency room, I almost always find that I am not at my best, usually in a bad mood, barking at someone who is trying hard not to tell me in a tactful way, how dumb I was. For ego’s sake, I prefer to avoid this whole scene and I have become good at it. Thus, idiot-proofing our effort is a primary consideration: safety first. Many people will tell you to use good old windshield washer fluid for its convenience and cost. I like that idea myself, but will never assume that just because we use it to smear bug guts on glass, it is safe to use in or near a combustion environment. I have seen enough racing mishaps to know that this kind of blind faith is a big mistake.

What we typically do with methanol is buffer it. We add water which helps to slow combustion (see the table at the bottom of the page). The right proportions of fuel-water, about 10-20% methanol, allow you to use it with zero net timing change requirement. Water alone tends to leave timing over-retarded.

The flash point of a chemical is the lowest temperature where it will evaporate enough fluid to form a combustible concentration of gas. The flash point is an indication of how easily a chemical may burn when exposed to a flame. Materials with higher flash points are less flammable than materials with lower flash points. Clearly then, adding water to methanol reduces its flammability danger as indicated in the table.

The table tells us, for example, that when ambient temperature is 75ºF or higher, a 50% mixture can be ignited with a flame or spark. If it is winter and 32ºF, you can not ignite pure methanol at all, you need at least 54ºF.
An excerpt from the MSDS published by the Aldon Corporation for handling methanol reads:

Class 1B flammable liquid. Burns with a clear, almost invisible flame, especially hard to see in strong sunlight. Methanol-water mixtures with 25% or more methanol are flammable. Avoid water streams which may splash and spread flaming liquid. Vapors are heavier than air and may flow along surfaces to distant ignition sources and flash back...

In other words, please do not fog methanol near your open-pilot gas water heater in your garage. Please don’t ask me how I know this.

You should recognize that windshield washer fluid comes in many concentrations of methanol, from zero to 40%, depending on its freeze rating. By and large, fire incidents with methanol mixtures are not common, we owe that to the high auto-ignition temps and dilution.

Applications

How you structure water cooling really depends on your goals. Performance junkies prefer the term drugs to describe chemical fuels in the charge airstream, used mainly for shorts bursts of high power. Haulers have a very different need: mainly dealing with heat soak and thermally protecting their equipment, with longevity higher up on the short list. Even large intercoolers are subject to efficiency erosion from heat soak. This happens when we stand on the pedal for longer than a few seconds while towing. The 500ºF heat from compression quickly consumes the heat storage capacity of the metal cooler, going from 150ºF to 250ºF in 30 seconds. There is going to be more value in augmented cooling after this heat soak sets in.

Towing

Earlier, I mentioned how fighter pilots used water to power turbo-charged flight to higher altitudes. Going where the enemy can not chase you is a nice advantage. The limitation to flight at higher altitudes is oxygen content and relying on the turbo-charger to provide it, after it has reached the RPM limit of its performance, is nothing but wishful thinking. At higher altitudes, this RPM (choke) limit is reached sooner for a given desired air flow. Water cooling allows the turbo to compress more air at that RPM limit: this provides the added power necessary to get higher, doing so also with less heat manufacture.

Elevation towing is a special opportunity to exploit water misting for a very similar result. Grade performance loss occurs in large part because the turbo loses efficiency and everything gets hotter and hotter as the pull progresses uphill into thinning atmospheric conditions. Soon, so much heat is produced that the radiator can no longer function correctly behind the CAC. This is the condition loathed by all heavy haulers, especially LLY owners.

Excess heat advances ignition. If you monitor cylinder pressure, you will see that the location of peak pressure pulls back toward TDC (an over-advance timing condition) and torque begins to drop off while cylinder pressure increases – a double negative that is bad for torque production.

Having an effective pre-turbo diesel water injection system at the end of your finger is the single handed cure-all for these symptoms of thermal feedback. Activating water injection, increases MAF, reduces the harmful heat production and puts LPP back where it needs to be, restoring torque optimization very quickly.

Smart Circuits-Dosing

If you see this as I do, having paid money for the methanol, then you will be inclined to set up the injection scheduling so that it only occurs when it will make the biggest difference. By avoiding spraying until conditions require it the most, you can easily reduce fluid consumption by 75%. Consumption occurs when thermal conditions will put it to the best possible use. The Mist-Miser mode, let’s call it.

Performance

There is not much point in injecting when heat is not being created, so fogging can be set up for high airflow production only (this is when the compressor is heating the most). In essence it will be used to extend top end full throttle performance.

A performance algorithm might be set to activate only when all of the following conditions are realized:

Boost greater than 25 PSI

Throttle greater than 95%

Intercooler outlet temps greater than 150ºF

(or some tweaked variation of this). We know this condition is creating a lot of induction heat for the engine. These conditions also insure that injection does not occur when conditions would be favorable for pooling and hydro lock – a failsafe.

ECT Control

Another user might be using diesel water injection to help keep ECT under control. In this case he might use:

ECT greater than 235

Boost greater than 15

TPS greater than 70%

Again, meeting all conditions will insure prudent consumption, knowing that added cooling is not necessary once you unload even if ECT is still high. Slow cooling is better for the truck anyway. The specific parameters you use should address all your specific concerns for safety, as well as imprudent use.

Introducing Induction Fog (I-Fog)

After two years, here is the patent pending result of being obstinate.

Working around the limitation of time and solid boundaries, means you have to use multiple, smaller capacity nozzles, locate them axially to the air stream – all flowing concentrically with the air stream – to reduce agglomeration and then make it easy and affordable to install. All from a single point feed and also be carefult not to introduce excess parasitic airflow resistance.

Supplies a variable amount of finely atomized fog, with capacity up to two liters pe/minute.

Uses multiple nozzles (up to 8), BUT only requires a single connection. The plumbing is all internal, no snake pit of tubes to hide or maintain.

Flow rate easily adjustable with various nozzle ratings.

Invisible to airflow-has no appreciable plumbing resistance due to its huge 4.75-inch size and aerodynamic low drag profile.

Fits all LBZ/LMM and all LLY with Induction Overhaul Kit.

Can also be used to supply Nitrous Oxide or alternative airborn fuels, propane, etc. – even in combination with each other.

To provide a significant difference to the cooling system and potential load capacity, a 60,000 BTU per hour cooling capacity is necessary. This has been demonstrated in past cooling system efforts. I-Fog is capable of 180,000 BTU per hour, which is enough cooling to air condition several of the homes on my street. This change alone can reduce your 375,000 BTU per hour induction related heat to 195,000. That is enough to silence the fan and reverse any heating tendency of your turbo-diesel, with just about ANY load you can find. The resulting power improvement through parasitic fan elimination, improved ignition quality, and increased compressor efficiency, when combined with the fuel value of 40% methanol, provides an on-grade benefit of 100 HP minimum. Add nitrous to one of the convenient tapped npt ports and the latent cooling can be increased further.

This is the perfect option to counter the influence of thermal feedback power erosion, to which I have dedicated myself over the last few years.

You can expect up to:

180,000 BTU/hr with water/methanol.

100,000 BTU/hr with water only.

100 HP increase (40% methanol).

350ºF EGT reduction.

Added cooling equivalent of a radiator and electric fan off of a 1500.